The recently remarkable development in mechatronics technology extensively requires various sorts of linear motion guide units, especially, linear motion guide units of the type using rolling elements of cylindrical roller, which are also required to meet with the maintenance-free operation where there is no need of lubricant replenishment for considerably long service life even under severe operating conditions. Most conventional linear motion guide units are composed of an elongated guide rail and a slider that moves relatively to the guide way by virtue of more than one rolling element, which is allowed to roll through a recirculating circuit that is made up of a load-carrying race defined between the guide rail and the slider, and a non-loaded area including a return passage and forward and aft turnaround passages made in the slider. With the linear motion guide units built in a diversity of machines, continuous application of lubricant on or between the load-carrying race and the rolling element is inevitable to continue maintaining an adequate lubricant film between the load-carrying race and the rolling element to keep them against metal-to-metal contact that might otherwise occur, thereby making sure of their high durability. To deal with the lubrication issue, most prior linear motion guide units have been ordinarily lubricated with periodic replenishment of lubricant so as to make certain of forming the lubricant film separating the rolling element from the circulating race. Recently advanced machines and instruments, nevertheless, are increasingly needed to make them virtually maintenance-free from many aspects of conserving energy as well as keeping running cost and maintenance cost of equipment reasonable. Correspondingly, the linear motion guide units built in the advanced machinery are also challenged to keep the consumption of lubricant to a minimum, along with keeping linear motion guide units virtually maintenance free.
In the commonly assigned Japanese Patent Laid-Open No. 2001-82469, there is disclosed a linear motion guide unit in which a return passage in a carriage of the slider is made of sintered resinous member of cellular or porous structure that is impregnated with lubricant to be applied on the rolling elements. The prior linear motion guide unit constructed as stated just earlier is comprised of an elongated guide rail, a slider movable lengthwise relative to the guide rail, and more than one rolling element allowed rolling into the load-carrying race defined between the guide rail and the slider from the non-loaded return passage cut in the slider, and vice versa in a recirculating manner. The return passage is constituted with a sleeve of sintered resinous member having cellular structure, which fits into a fore-and-aft hole made in the carriage of the slider. Oily lubricant or grease once soaked in the sintered resinous member preparatory to fit into the carriage is reserved or held in the cells or pores in the cellular structure. Oily ingredient of the lubricant is constantly applied on the rolling elements while they roll through inside the sleeve, and oil films around any rolling elements get lubricating smoothly the load-carrying surfaces or raceway grooves as the rolling elements run through load race, with accompanying reduced maintenance.
Another commonly assigned Japanese Patent Laid-Open No. H09-72335 discloses a linear motion guide unit in which a sleeve for a return passage fits into a fore-and-aft hole made in a carriage of the slider to provide the return passage. The sleeve is made easier to experience elastic deformation to absorb the frictional resistance occurring on the rolling elements, thereby ensuring smooth running of the rolling elements. With the linear motion guide unit constructed as recited just earlier, the rolling elements are made in the form of cylindrical roller while the return passage is defined inside the sleeve that fits closely into the return hole cut in the carriage. The sleeve is made it possible to get elastic deformation, ensuring smooth traveling of the slider. In the linear motion guide unit recited above, especially, an ample clearance is left between the circular surface inside the fore-and-aft hole for the return passage and the outside surface around the middle area of the sleeve to allow the sleeve to get elastically deformed therein and also reserve lubricant therein.
A further another sort of linear motion guide means is disclosed in the commonly assigned Japanese Patent Laid-Open No. H05-209617, in which a spacer piece is installed in an end cap to provide a turnaround passage inside the end cap. The spacer piece installed in the end cap to have the turnaround passages therein is made on the curved surface thereof with a turnaround race where two lines of lubricant reservoir grooves are cut to get lubricant escaping through there. With the linear motion guide unit recited above, the end cap is made concave to provide a recess in preparation for the turnaround passage while the spacer piece having the turnaround race around there fits into the recess to define the turnaround passage between them. The spacer piece is made on the turnaround race thereof with lubricant reservoir grooves, which extend in the running direction of the rolling elements to retain the lubricant therein while getting the lubricant to escape from there.
With the linear motion guide unit in which cylindrical rollers are selected as the rolling elements, nevertheless, alignment problems to guide rollers in good rolling order without leaning in rolling posture are more encountered, compared with the construction using balls. Besides, the cylindrical rollers have to be guided not only on their circular rolling surfaces, but also on their axially opposite end surfaces. Conventionally, there is no linear motion guide unit constructed to meet with an aspect of allowing the rollers to roll through the recirculating circuit over a long-lasting service life with adequate application of lubricant, making certain of steady reliability of the maintenance-free on lubricant application.
With the linear motion guide units in which the cylindrical rollers are selected for the rolling elements, moreover, as there is some tendency to displace much lubricant from the load-carrying race compared with balls, it is needed for the aspect of ensuring maintenance-free operation to sustain more lubricant in the recirculating circuit for the rollers than for the balls. In addition, the cylindrical rollers should be guided in good order without leaning in rolling posture, that is to say, the cylindrical rollers have to be guided not only on their circular surfaces, but also on their axially opposite end surfaces.
The prior linear motion guide unit disclosed in the Japanese Patent Laid-Open No. H05-209617 recited earlier is favorable for the cylindrical roller larger in diameter, but unsuited for the slender roller, which is easier to lean to get more failure in recirculating performance. Thus, the prior linear motion guide unit would involve the alignment problem where the cylindrical rollers are prone to lean to get more failure in recirculating performance that would ensure the steady recirculation to the rollers for long-lasting service period with maintenance-free condition for lubricant replenishment.
With the prior linear motion guide units disclosed in the Japanese Patent Laid-Open No. 2001-82469 recited earlier, the return passage made in the carriage of the slider is defined by just sintered resinous member of cellular geometry, which is lack of mechanical stiffness enough to guide steadily the cylindrical rollers. The rollers, as opposed to the balls, need functioning on line-rolling contact around their circular surfaces without getting tilted in rolling posture. In other words, the rollers have to be not only born against their circular surfaces, but also guided in sliding manner on their axially opposite ends to get the slider moved steadily with smoothness, ensuring the long-lasting service life with stability. Thus, the prior linear motion guide units of the sort in which the return passage is made of only sintered resinous member of cellular geometry, because there is a scarcity of mechanical stiffness in the sintered resinous member, have been unsuited for making certain of smooth recirculation of the rollers.
There, advanced technology has come to hope any linear motion guide unit in which the sleeve to define the return passage in the carriage of the slider is much raised in mechanical stiffness, even with simple in construction and easier to fit it into the slider as well as making sure of positive lubricant application to the rolling elements to render the maintenance-free operation steadier.